1. Field of the Invention
This invention relates to bearings of the type utilized in rotary machinery, and more specifically to oil damped bearings incorporated spring stabilizers.
2. Description of the Prior Art
In many types of rotary machines, rotors mounted therein experience vibration of high amplitude. Such vibration causes large forces to be transmitted across the bearings between the rotor and the machine housing. If left unchecked, higher than normal stresses in the bearings are generated and premature failure of the bearings results.
Vibration may be caused by both synchronous and non-synchronous stimuli. Synchronous stimuli are associated with unbalanced weight on the rotor as may result in the manufacture or assembly of components, or which may occur through internal damage during operation of the machine. Non-synchronous excitation is a self-exciting phenomenon resulting from variable loadings on the rotor. Such variable loading frequently occurs in fluid film bearings, or may result from varied aerodynamic loading on one or more of rotor members.
One effective means for damping excitation in rotors is known as film damping. In film damping an incompressible fluid such as oil is flowed in an annulus around the outside of the bearing. The bearing is free to move orbitally about the annulus. The orbital motion of the bearing in the damping fluid generates a hydrodynamic pressure which resists further displacement. Shearing of the fluid occurs and, in a well designed system, effective damping of vibration results.
Oil damped bearings have been known in industry for some time. One early showing in 1952 which will be useful in understanding the concepts disclosed herein, is set forth in U.S. Pat. No. 2,602,009 to Barlow et al entitled, "Bearing Mounting". In Barlow et al a plurality of chambers are formed between an inner sleeve and an outer sleeve which is spaced radially from the inner sleeve. Each chamber is in communication with adjacent chambers and is filled with a viscous fluid. Should the shaft supported by the bearing tend to move orbitally, the respective volumes of the chambers begins to vary. Oil is caused to flow between adjacent chambers and orbital movements of the shaft become damped.
Since the early development of film dampers, improved support structures combining spring damping with the film damping have been developed and used. In such apparatus, the inner ring of a film damper is cantilevered from a ridged support structure. One typical illustration of such a construction is shown in NASA Technical Note NASA TN D-7892 by Cunningham et al entitled "Design of an Oil Squeeze Film Damper Bearing for a Multimass Flexible-Rotor Bearing System". Other similar structures are shown in U.S. Pat. No. 4,046,430 to Buono et al entitled "Damped Inner Shaft Bearing and Stabilizer"; U.S. Pat. No. 3,979,155 to Sood et al entitled "Flexible Damped Bearing Support"; U.S. Pat. No. 3,994,541 to Geary et al entitled "Bearing Assembly"; and U.S. Pat. No. 4,027,931 to Streifert entitled "Flexible Damped Bearing Support".
Notwithstanding the advanced state of the damper art as represented by the above publication, scientists and engineers involved in the design of rotary machinery continue to search for structures having yet improved damping qualities or reduced physical size.